1. Field of the Invention
This invention relates in general to a method and an optical tool that enables physicians and surgeons to quickly and efficiently measure or establish proper alignment and angle configuration between replacement skeletal joints and skeletal tissue without utilizing mechanical implements that would otherwise be attached to the skeletal structure during a surgical replacement procedure. More specifically, the specification describes one form of the invention that relates to a method and an optical tool that generates and projects a plurality of linear laser beams, which beams are projected onto the limb or other body structure of a surgical patient to establish a reference pattern which the surgeon follows to achieve optimal alignment and ideal angle measurements for seating and insertion of a replacement skeletal joint.
2. Description of the Related Art                A. The Current Art for Surgically Creating an Accurately-Measured Angle and Seat for a Replacement Skeletal Joint.        
By conservative estimates, within the United States alone, hundreds of thousands of skeletal joints are replaced by skilled orthopedic surgeons annually. Skeletal joint replacement surgical specialists each undergo several years of training and routinely perform hundreds of joint replacement procedures every year. The medical pathologies that necessitate joint replacements are many and varied, and include injury to the affected skeletal joint, degradation of supporting structures within the joint due to aging or illness, structural misalignment of the joint due to muscular, skeletal, and other imbalances, and excess stress to the affected joint resulting from repetitive use at the patient's workplace or other environment.
Notwithstanding the fact that a joint replacement surgical procedure is technically and medically complex, and further that the procedure demands years of surgical training, the process lends itself to a straightforward description and explanation. By way of example, the following description summarizes the steps taken by the surgeon to replace a knee joint. The surgeon first makes an incision and exposes the knee joint that will be replaced. Once exposed, the surgeon separates the two long bones that meet to form the knee joint, namely, the femur, which extends from the hip joint to the knee, and the tibia, which extends from the knee to the ankle. The surgeon then affixes an external alignment device to the femur by first, establishing a canal in the lower end of the femur to receive a locating device. Next, the surgeon inserts the locating device into the canal.
The alignment device is generally situated in a parallel orientation to the surgical patient's femur, and is attached external to the patient's leg. The combination of the locating device and alignment device thus creates an external structure which the surgeon uses as a guide to marry the replacement joint to the existing bone. The surgeon is working in three dimensions, and it is critical that the alignment and locating devices be affixed properly to give the surgeon the best guidelines for the next step of the procedure.
The locating device generally includes a cutting block, which includes several die-cuts, or jigs, that are used as guides for a surgical saw. The surgeon will use this saw to sever or resect the lower portion of the femur, which creates a platform of exposed bone tissue on the femur that will support the upper portion of the replacement joint. It is critical for the surgeon to make this cut at the proper angle to receive the replacement joint. The surgeon's ability to craft a proper angle on the receiving end of the femur is a critical component in the relative success of the surgical procedure. Because the angle of the cut is so critical, the surgeon will generally devote substantial amounts of time to setting the alignment device and confirming that it is properly oriented to the patient's bone structure and that the dies or jigs are lined up to guide the saw in a manner that creates the ideally-angled platform to receive the replacement joint.
The surgeon will perform a similar procedure on the patient's tibia. Specifically, the surgeon exposes the upper end of the tibia, attaches an external tibial alignment device, and attaches a cutting platform that includes analogous jigs or dies to allow the surgeon to cut an ideally-angled platform at the top of the patient's tibia to receive the replacement joint. As with the femoral alignment device, the external tibial alignment device is affixed in a generally-parallel orientation to the patient's tibia, and the angle of the cut is generally measured as an angle to the tibia
As with the setting of the alignment device for the femur, the surgeon will also devote a substantial amount of time during the surgical procedure to affix the tibial alignment devices properly to create an ideal lower platform to receive the replacement joint. In any surgical procedure, however, particularly where the surgical patient is anesthetized with general anesthesia, the surgeon is balancing competing interests, namely, devoting sufficient time to performing the surgical procedure and achieving proper alignment of the replacement joint, while moving expeditiously so as not to keep the patient anesthetized any longer than is absolutely necessary. Accordingly, any methods or techniques that would enhance the surgeon's accuracy to perform a joint replacement procedure while simultaneously expediting that procedure would be highly desired.
This mechanical alignment process is the predominant methodology that is currently used in surgical joint replacements. Technicians and surgeons are developing computer-guided alignment systems, including scanning cameras that take an image of the joint and surrounding skeletal tissue and accompanying software that guides a surgical saw to make the desired cut at a correct angle. These systems are still in an experimental phase, and as such are cost-prohibitive for all but the most well-financed medical facilities. Moreover, these systems require extensive equipment installations and reconfigurations of surgical facilities. While they may be common place in future designs, it is unlikely that they will find rapid or common acceptance within the near term.                B. Commercially-available Laser-line Projection Devices.        
Laser-guided projection tools and guide devices have been commercially available to the construction and building trades for many years. These tools are configured to project an illuminated bright laser line on any horizontal or vertical surfaces to give the tradesman a guideline during a construction process.
In operation, the tradesman will set the laser-projection device on a surface or support stand in the region in which he or she is working. The projection device will generally have two or three leveling devices, which devices are most frequently small fluid-filled vials that also contain a single air bubble. These hydraulic vials will be marked with a plurality of hatched lines. Each of the vials is situated along one axis of a three-dimensional configuration. The tradesman then adjusts the overall level of the device by turning set screws that variously raise or lower portions of the device. When the device itself is level, the single air bubbles in the glass vials will be situated in the exact center of the hatch-marks etched into the vials.
The projection device, which is most typically battery-operated, will then be set to project one or more bright lines across a surface. The line itself will generally be projected to be level and square in comparison to other features in the room. Alternately, if the tradesman desires, the projected line can be set at an angle that is measured against gauges on the projection device.
Although these devices generally project only a single line, it is a simple matter of optics to configure the laser projection device to project two or more bright lines. The lines can be projected to intersect each other at various angles or to run parallel along any given surface. In this manner, the tradesman can project patterns of lines across any surface that will be used as guides for the tradesman's craft.